The Effect Of Laser Deformation On Fatigue
Properties Of Automotive Dual Phase Steel
Author(s)
A. Els-Botes, P. J. McGrath & D. G. Hattingh
Abstract
It became evident from previous research that the fatigue strength of wheel
centre discs decreases as much as 83% during the manufacture (first production
stage) of the automotive wheel [1, 2]. This information was the driving force in
obtaining an alternative forming process in order to maintain the high fatigue
strength of the metal. The laser forming/deforming process was chosen because
of its ease of automation and reproducibility. It was found that it was possible to
deform dual phase steel specimens, employing various laser parameters, to the
same radius of curvature as that of the first production stage of wheel centre
discs. Microstructural analysis indicated a change of the original microstructure
due to the heat generated by the laser beam. The original martensite/ferrite
microstructure transformed to various transformation phases of the steel, like
bainite and ferrite/carbide aggregate. These microstructural changes are
concentrated on the surface over which the laser beam radiated. Grain growth
was also observed and is an important consideration as large grains are
considered to embrittle a material. Fatigue testing of the laser formed specimens
revealed that the process has potential to be used as a production stage, providing
that line energy and beam diameter is carefully controlled. The laser formed
specimens formed by employing a 1.5kW laser power showed results very
similar to those obtained by specimens formed be means of a pure bend process.
Although the results obtained indicated that laser forming has the possibility of
being employed as a deformation process, the fatigue properties of the laser
formed specimens were inferior compared to the original un-deformed material.
It was also determined that the hardness profile along the length of the specimens
showed a variation that could lead to a metallurgical notch. The hardness was at
a maximum with the position corresponding to the centre of the laser beam with
the lowest hardness obtained in the region between two consecutive laser heat
lines.
Keywords: laser deformation, laser forming, laser bending, fatigue, dual phase
steel.
Keywords
laser deformation, laser forming, laser bending, fatigue, dual phase
steel.
Related Book
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